Many human tissues contain extensive systems of biological tubes, including glands, the urogenital and gastrointestinal tracts, the respiratory tract, and the vascular system. Despite their importance, much remains unknown about the molecular mechanisms involved in tube development. There is an urgent need to increase knowledge of tubulogenesis, not only so that we may understand normal development, but also to devise better ways to prevent and treat birth defects that result from tubes not forming properly, including neural tube closure defects and polycystic kidney disease. The research proposed here involves investigating the role of an actin regulator, tropomodulin, in the regulation of tube development. Tropomodulins are one of the few proteins known to cap and regulate the slow growing ends of actin filaments. The model system that will be used is the C. elegans intestine, which is a simple, optically transparent tube that forms by a cord-hollowing mechanism similar to that used by human capillaries and renal tubules. Thus, studying tubulogenesis in the C. elegans intestine is likely to give more global insights into the molecular mechanisms that underlie this process. Initially, the subcellular localization of TMD-1/tropomodulin in the intestine will be assessed;and the effects of tmd-1 loss-of-function on intestinal morphogenesis will be determined. Exciting preliminary studies indicate an important role for TMD-1 in regulating tube diameter. TMD-1 may regulate lumen diameter by modulating actomyosin contractility, cooperating with the actin-spectrin cytoskeleton to provide mechanical strength, or by regulating vesicle trafficking. Each of these possibilities will be systematically tested. Finally, by screening for enhancers of a tmd-1 mutant allele, tm724, proteins that functionally interact with tmd-1 will be identified and subsequently characterized, which will give more information on the role of actin in tube development. Techniques that will be used to accomplish these experiments include immunostaining, confocal imaging, live 4D Nomarski videomicroscopy, analysis of intestinal ultrastructure via transmission electron microscopy, and functional genomics screening using RNA interference. This research will be the first to establish a role for tropomodulins in tube morphogenesis and will give significant mechanistic insights into their roles in this important developmental process.